1. Field of the Invention
The present invention relates to a method of shaping a foam article having opposite sides that are formed, at least in part, in a milling operation.
2. Background Art
A wide variety of shaped articles may be made from foam polymeric materials. A popular polymeric foam material is foam polyurethane. Polyurethane foam may be provided in a range of densities and, depending upon its density and composition, may have varying degrees of elasticity. If a foam article is to be shaped on opposite sides, increased flexibility can make it difficult to support the foam body as it is shaped. One example of a foam article is a foam bun for a vehicle seat. Other foam bodies may include furniture cushions, toys, and padding for vehicle interior parts.
Foam buns for vehicle seats are normally produced in production processes in which a two-component polyurethane reactant mixture is poured into a specially designed mold that forms the seat body in situ to the desired size and shape. Pre-production or prototype foam buns must be made without the benefit of a production mold due to the relatively high cost of making a mold. Frequently, an automotive manufacturer will require several prototype designs for evaluation prior to committing to a final production design. Once a final production design is selected, a mold can be made based upon the approved prototype design.
A block of pre-formed foam may be cut with a knife or formed with a programmable milling machine to make pre-production samples and prototypes. While this approach eliminates the need for an expensive molding tool, it is difficult to accurately cut a block of flexible foam due to the tendency of the foam material to be distorted as pressure is applied to the foam block. This is particularly problematic when one side of the foam block has been cut to a desired contour and then an opposite side must be shaped while the previously shaped side supports the foam block.
One proposed solution to the above problem is disclosed in U.S. Pat. No. 6,588,086 that issued to Trybus (“the '086 patent”). In the method disclosed in the '086 patent, one side of a foam block is milled to the desired contour creating loose granular waste that would normally be vacuumed to a waste receptacle. According to the method disclosed in the '086 patent, the loose granular fill material is placed back in the cavity formed when the first side is milled. A sheet is then secured over the loose granular film material to hold the fill material in place in the cavity while the second or opposite side of the foam block is shaped. The loose granular fill material helps to reduce distortion and support the foam block. However, it is time consuming to pack the cavity with the granular fill material, cover it with a sheet of material, shape the second side of the foam block material, and then remove the granular material. The loose granular material is difficult to control if not contained and must be frequently removed from clothing and surrounding areas. In addition, there is a possibility that insufficient or excessive granular fill material may be loaded into the cavity that can cause dimensional variation in the finished product.
There is a need for a quick and accurate process for shaping a foam article that is contoured on opposite sides from a block of foam. There is a further need for a process wherein computer-aided design data can be used as a starting point for optimizing control of a programmable milling machine to form a shaped foam article that is shaped on opposite sides to design tolerances. There is also a need for an efficient labor-saving process for forming opposite sides of a foam article.
The present invention addresses the above problems and needs as summarized below.